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Re: [webrtc-pc] addTransceiver woes

From: henbos via GitHub <sysbot+gh@w3.org>
Date: Thu, 28 Dec 2017 20:51:53 +0000
To: public-webrtc-logs@w3.org
Message-ID: <issue_comment.created-354356092-1514494312-sysbot+gh@w3.org>
About the question for what a=msid to use when we don't have a track.id to announce...

It is already the case with replaceTrack() that the sending track.id does NOT necessarily correspond to the a=msid line. Example:
```
sender = pc1.addTrack(track1);  // a=msid with track1.id announced in SDP
negotiate
sender.replaceTrack(track2);  // seamlessly change which track to send, same a=msid as before
```
In fact, if we try to use track.id we can end up with multiple senders trying to use the same ID... the ID needs to be unique to the sender, not to whatever track happens to be sending at the moment.

So what should happen?
addTransceiver() creates a sendrecv transciever with a random id announced in the SDP. The receiving end is ready to receive and replaceTrack() works without renegotiation, just like it would have if addTrack() was used.

That is, the spec is already correct for addTransceiver(). But if a=msid takes the track's ID, we might need to file a bug on track ID collisions...

-- 
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Received on Thursday, 28 December 2017 20:52:01 UTC

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